This invention relates to an apparatus for the exposure of a recording carrier to show alpha numeric characters or faces having a foreground pattern which contrasts relative to a background pattern. The exposure in this type of apparatus is generally accomplished with an intensity modulated scanner whose beam is moved along scanning lines above the recording carrier in the direction of the lines. These systems generally comprise a switch-over control logic for driving a modulator switch connected to a scanner heam modulator at the characters or face borders.
In a number of graphic applications, it is desirable to expose characters or alpha numeric characters, as is common, in a manner such that they all completely black on a white background, or with a reverse contrast on a recording carrier as white on a black background. The carrier is exposed to generate the characters by scanning along scanning lines particularly running in the direction of the lines. In the case of printed matter in advertisements or in form printing, area effects are generated on the exposed recording carrier, by filling defined area portions of the exposed recording carrier with small regular structures i.e., a pattern. Depending on the size and shape of these structures, they may be arranged to create rasters, shadings, signatures or similar structures. In the following description, these structures will generally be referred to as patterns. By definition, such patterns will also include half tone simulations where the pattern consists of abstract graphic elements, particularly small points, the size and distance of which are below the limit at which they can be individually perceived by the observer's eye as a half tone perception. In order to build a structure, patterns having abstract graphic elements may be used, the raster width of which in this case has to be so large that the structures can be perceived. The graphic elements of the patterns may finally also be regularly arranged signatures, for example, symbols on maps.
Up to now, such patterns have as a rule been generated independently from the typographic design, and then have subsequently been copied together with the typographic design. This process however is complicated, time consuming and requires extreme care.
It has therefore been attempted to simultaneously expose, by means of a so-called direct exposure of a recording carrier including alpha numeric characters or faces, a background pattern or foreground pattern. This technique is conventional and such a system is available as a form typesetting system from Purup Electronics under the trade name "Purup 4000".
Recently, it has also been attempted to so further develop a typographic laser exposer that can expose both raster as well as background patterns. By means of the laser exposer, technical rasters such as grey tone areas in forms, tables, price lists, prospectusses, etc. are displayed in various shapes and different tone grades. To this end, hardware raster generators have been developed which are loaded with corresponding patterns which are calculated prior to the recording, i.e., exposure, by the software, and are regularly repeated during exposure. The parameters defined by the operator for raster type, percentage area coverage, raster width and optimizing functions are automatically stored in one of the raster generators. In turn, they control, in relation to the data for the defined area sizes, X and Y positions and the type of display, i.e., script positive, negative or rastered on full tone or raster areas, the recording. Each raster point consists of micro elements or picture elements generally identified as pixels. Such a system is also conventional and commercially availahle from Linotype GmbH under the trade name "Linotronic 300". The "Linotronic 300" exposure system includes raster and background--compare Press Release features of the type well known to those of ordinary skill in this art.
One problem in the embodiment of such an exposure system including raster and background pattern is that a plurality of different patterns have to be provided for a comprehensive application, of which a few have to be used, during the line scanning of the recording carrier by the scanning beam, for the intensity modulation thereof. In this connection, it should be taken into consideration that at each line border, i.e., in the transition from the background pattern of an alpha numeric character to its inner foreground pattern, a change in the pattern occurs. In the case of a common black and white representation of the alpha numeric characters, when changing the pattern, one need switch the scanner beam modulator only from a black level to a white level of a static signal source, or vice versa. This switching-over required only a bit of airformation. In this regard, it is noted that the term "black level" or "white level" are conventional terms well known to those of ordinary skill in the art of computerized phototypsetting.
If a plurality of signal sources including raster generators are available for the generation of different patterns, it is obvious to expand the modulator switch which connects the scanning beam modulator at each point of intersection, i.e., at a border of an alpha numeric character or a face with one of the various signal sources, in a manner corresponding to the number of signal sources. Considering that in the course of a scanning line covered by the scanning beam a plurality of points of intersection are required, as a rule, to be scanned, the control of such an expanded modulator switch requires the generation, transfer and processing of a high data rate i.e., data amount per unit of time, which represents the successive points of intersection, where the points of intersection include a position on the scanning line, at which time switch-over of the modulator switch should occur, and at the same time should describe that pattern of a plurality of patterns available with the foreground pattern signals with background pattern signals of which the scanning beam modulator has to be supplied over the next scanning line section. Of course such processing typically requires a large amount of time, thus delaying the speed of operation of the device.